Alexander said: “What we have seen in recent years is a huge cutting back of that Prevent programme under the current Government.

“I hope that in the light of these very worrying developments the Government will think about its approach to Prevent.”

He also said the public would want to know why no preventative action was taken if Aqsa got in touch with the London schoolgirls.

Alexander added: “I think many of us will want to know why alarm bells weren’t ringing when it turned out that the Glasgow schoolgirl now in Syria contacted the three London schoolgirls who sadly are now unaccounted for.

“We need some answers in relation to the contact there’s been between the Glasgow schoolgirl and the London schoolgirls, but the overriding priority today must be to make contact with these three London schoolgirls who all of us hope are still in Turkey and not within Syria.”

Shamima tweeted Aqsa on Feb 15 with the message: “follow me so i can dm [direct message] you back.”

There has been no public activity on Aqsa’s Twitter account since December 23.

Douglas Alexander (Image: Chris Ison/PA Wire)

But lawyer Aamer Anwar said her family want to know how the girls could have been allowed to travel to Turkey alone.

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He said: “They were full of horror and anger that their daughter may have been involved in the recruitment and encouragement of these young girls to go out and join her and ISIS in Syria.

“The family have been heartbroken for over 15 months, totally distraught, torn to pieces and they keep wondering how much more misery can Aqsa bring to their lives.

“But the fact now their daughter is involved, potentially, in tearing apart other families is something that is beyond the pale for them.”

Anwar, speaking on BBC Breakfast, said the family were in a state of “incredulity” that the girls managed to leave the UK despite the Twitter contact.

He said: “We are aware from contacts with Special Branch and the police that her social media contact is regularly checked and regularly monitored.

“The idea now that a young 15 year-old should make contact with Aqsa - who is regarded as a terrorist, a member of ISIS - yet no action is taken, the family of that young girl do not have the customary knock on the front door or the fact the three girls manage to reach an airport.”

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Anwar expressed alarm that Special Branch or the UK Border Agency did not stop the girls when they turned up unaccompanied at the airport bound for Turkey.

He added: “Obviously the family are deeply distressed and angry and they want answers.

“They are thinking: ‘How many other families is this happening to?’”

Anwar also confirmed the family have had “intermittent contact” with Aqsa since she fled Scotland.

The family released a statement on Saturday after their daughter returned to the headlines.

In a direct message to Aqsa, they said: “You are a disgrace to your family and the people of Scotland, your actions are a perverted and evil distortion of Islam.

“You are killing your family every day with your actions, they are begging you stop if you ever loved them.”

The statement also said the security services have “serious questions to answer”.

It added: “Aqsa’s social media has been monitored since she disappeared over a year ago, yet despite alleged contact between the girls and Aqsa, they failed to stop them from leaving the UK to Turkey, a staging post for Syria.”

Privately-educated Aqsa is reported to have encouraged terrorist acts via a Twitter account under the name Umm Layth.

She travelled through Turkey to Aleppo in Syria in November 2013 and was reported missing to police.

Before disappearing she attended Craigholme School then Glasgow Caledonian University, where she dropped out of her diagnostic radiography course to travel to Syria,

Kadiza, Shamima and Amira, who all attended Bethnal Green Academy in east London, flew from Gatwick to Turkey after telling their parents they were going out for the day.

It is not clear whether the London girls - all “star GCSE pupils” - have crossed from Turkey into Syria.

Police said they had been interviewed after another girl from their school went to Syria in December, but nothing had indicated they were at risk.

The girls’ families have all made public pleas for them to return home.

Prevent is one of the four elements of CONTEST, the Government’s counter-terrorism strategy, and is designed to stop people becoming terrorists or supporting terrorism.

The partnership initiative provides practical help to prevent individuals from being drawn into terrorism and aims to identify those most at risk from radicalisation.

It funds a specialist police unit which works to remove online content that breaches terrorist legislation, supports community campaigns to combat extremist propaganda and aims to prevent apologists for extremism from entering the country.

The programme’s overseas activity is concentrated on Pakistan, the Middle East and East Africa where radicalising activity can have a direct impact on communities in the UK.